mountains," mountains of this kind are not formed by the gradual
accumulation of ejected currents of lava, but their origin seems rather to
be a general consequence of the sudden elevation of soft masses of trachyte
or labradoritic augite. The amount of the elevating force is manifested
p 229
by the elevation of the volcano, which varies from the inconsiderable height
of a hill (as the volcano of Cosima, one of the Japanese Kurile islands) to
that of a cone above 19,000 feet in height. It has appeared to me that
relations of height have a great influence on the occurrence of eruptions,
which are more frequent in low than in elevated volcanoes. I might instance
the series presented by the following mountains: Stromboli, 2318 feet;
Guacamayo, in the province of Quixos, from which detonations are heard
almost daily (I myself often heard them at Chillo, near Quito, a distance of
eighty-eight miles); Vesuvius, 3876 feet; Aetna, 10871 feet; the Peak of
Teneriffe, 12,175 feet; and Cotopaxi, 19,069 feet. If the focus of these
volcanoes be at an equal depth below the surface, a greater force must be
required where the fused masses have to be raised to an elevation six or
eight times greater than that of the lower eminences. While the volcano
Stromboli (Strongyle) has been incessantly active since the Homeric ages,
and has served as a beacon-light to guide the mariner in the Tyrrhenian Sea,
loftier volcanoes have been characterized by loong intervals of quiet. Thus
we see that a whole century often intervenes between the eruptions of most
of the colossi which crown the summits of the Cordilleras of the Andes.
Where we meet with exceptions to this law, to which I long since drew
attention, they must depend upon the circumstance that the connections
between the volcanic foci and the crater of eruption can not be considered
as equaly permanent in the case of all volcanoes. The channel of
communication may be closed for a time in the case of the lower ones, so
that they less frequently come to a state of eruption, although they do not,
on that account, approach more nearly to their final extinction.
These relations between the absolute height and the frequency of volcanic
eruptions, as far as they are externally perceptible, are intimately
connected with the consideration of the local conditions under which lava
currents are erupted. Eruptions from the crater are very unusual in many
mountains, generally occurring from lateral fissures (as was observed in the
case of Aetna, in the sixteenth century, by the celebrated historian Bembo,
when a youth*), whenever the sides
p 230
of the upheaved mountain were least able, from their configuration and
position, to offer any resistance.
[footnote] *Petri Bembi Opuscula ('Aetna Dialogus'), Basil, 1556, p. 63:
"Quicquid in Aetnae matris utero coulescit, nunquam exit ex cratere
superiore, quod vel eo inscondere gravis materia non queat, vel, quia
inferius alia spiramenta sunt, non fit opus. Despumant flammis urgentibus
ignei rivi pigro fluxu totas delambentes plagas, et in lapidem indurescunt."
Cones of eruption are sometimes uplifted on these fissures; the larger ones,
which are erroneously termed 'new volcanoes', are ranged together in line
marking the direction of a fissure, which is soon reclosed, while the
smaller ones are grouped together covering a whole district with their
dome-like or hive-shaped forms. To the latter belong the 'hornitos de
Jorullo',I the cone of Vesuvius erupted in October, 1822, that of Awatscha,
according to Postels, and those of the lava-field mentioned by Erman, near
the Baidar Mountains, in the peninsula of Kamtschatka.
[footnote] See my drawing of the volcano of Jorullo, of its 'hornitos', and
of the uplifted 'malpays', in my 'Vues de Cordilleres', pl. xliii., p. 239.
[Burckhardt states that during the twenty-four years that have intervened
since Baron Humboldt's visit to Jorullo, the 'hornitos' have either wholly
disappeared or completely changed their forms. See 'Aufenthalt und Reisen
in Mexico in 1825 und 1834'.] -- Tr.
When volcanoes are not isolated in a plain, but surrounded, as in the double
chain of the Andes of Quito, by a table-land having an elevation from nine
to thirteen thousand feet, this circumstance may probably explain the cause
why no lava streams are formed* during the most dreadful eruption of ignited
scoriae accompanied by detonations heard at a distance of more than a
hundred miles.
[footnote] * Humboldt, 'Essaii sur la Geogr. des Plantes et Tableau Phys.
des Regions Equinoxiales', 1807, p. 130, and 'Essai Geogn. sur le Gisement
des Roches', p. 321. Most of the volcanoes in Java demonstrate that the
cause of the perfect absence of lava streams in volcanoes of incessant
activity is not alone to be sought for in their form, position, and height.
Leop. von Buch, 'Descr. Phys. des Iles Canaries', p. 419; Reinwardt and
Hoffmann, in Poggened., 'Annalen.', bd. xii., s. 607.
Such are the volcanoes of Popayan, those of the elevated plateau of Los
Pastos and of the Andes of Quito, with the exception, perhaps, in the case
of the latter, of the volcano of Antisana. The height of the cone of
cinders, and the size and form of the crater, are elements of configuration
which yield an especial and individual character to volcanoes, although the
cone of cinders and the crater are both wholly independent of the dimensions
of the mountain. Vesuvius is more than three times lower than the Peak of
Teneriffe; its cone of cinders rises to one third of the height of the whole
mountain, while the cone of cinders of the Peak is only 1/22d of its
altitude.
[footnote] * [It may be remarked in general, although the rule is liable to
exceptions, that the dimensions of a crater are in an inverse ratio to the
elevation of the mountain. Daubeney, op. Cit., p. 444.] -- Tr.
In a much higher volcano than that of Teneriffe, the Rueu Pichincha, other
relations occur
p 231
which approach more nearly to that of Vesuvius. Among all the volcanoes
that I have seen in the two hemispheres, the conical form of Cotopaxi is the
most beautifully regular. A sudden fusion of the snow at its cone of
cinders announces the proximity of the eruption. Before the smoke is
visible in the rarefied strata of air surrounding the summit and the opening
of the crater, the walls of the cone of cinders are sometimes in a state of
glowing heat, when the whole mountain presents an appearance of the most
fearful and portentous blackness. The crater, which, with very few
exceptions, occupies the summit of the volcano, forms a deep, caldron-like
valley, which is often accessible, and whose bottom is subject to constant
alterations. The great or lesser depth of the crater is in many volcanoes
likewise a sign of the near or distant occurrence of an eruption. Long,
narrow fissures, from which vapors issue forth, or small rounding hollows
filled with molten masses, alternately open and close in the caldron-like
valley; the bottom rises and sinks, eminences of scoriae and cones of
eruption are formed, rising sometimes far over the walls of the crater, and
continuing for years together to impart to the volcano a peculiar character,
and then suddenly fall together and disappear during a new eruption. The
openings of these cones of eruption, which rise from the bottom of the
crater, must not, as is too often done, be confounded with the crater which
incloses them. If this be inaccessible from extreme depth and from the
perpendicular descent, as in the case of the volcano of Rucu Pichincha,
which is 15,920 feet in height, the traveler may look from the edge on the
summit of the mountains which rise in the sulphurous atmosphere of the
valley at his feet; and I have never beheld a grander or more remarkable
picture than that presented by this volcano. In the interval between two
eruptions, a crater may either present no luminous appearance, showing
merely open fissures and ascending vapors, or the scarcely heated soil may
be covered by eminences of scoriae, that admit of being approached without
danger, and thus present to the geologist the spectacle of the eruption of
burning and fused masses, which fall back on the ledge of the cone of
scoriae, and whose appearance is regularly announced by small wholly local
earthquakes. Lava sometimes streams forth from the open fissures and small
hollows, without breaking through or escaping beyond the sides of the
crater. If, however, it does break through, the newly-opened terrestrial
stream generally flows in such a quiet and well-defined course, that the
deep valley, which we term the crater, remains accessible
p 232
even during periods of eruption. It is impossible, without an exact
representation of the configuration -- the normal type, as it were, of
fire-emitting mountains, to form a just idea of those phenomena which, owing
to fantastic descriptions and an undefined phraseology, have long been
comprised under the head of 'craters, cones of eruption', and 'volcanoes'.
The marginal ledges of craters vary much less than one would be led to
suppose. A comparison of Saussure's measurements with my own yields the
remarkable result, for instance, that in the course of forty-nine years
(from 1773 to 1822), the elevation of the northwestern margin of Mount
Vesuvius ('Rocca del Palo') may be considered to have remained unchanged.*
[footnote] *See the ground-work of my measurements compared with those of
Saussure and Lord Minto, in the 'Abhandlungen der Akademie der Wiss. zu
Berlin' for the years 1822 and 1823.
Volcanoes which, like the chain of the Andes, lift their summits high above
the boundaries of the region of perpetual snow, present peculiar phenomena.
The masses of snow, by their sudden fusion during eruptions, occasion not
only the most fearful inundations and torrents of water, in which smoking
scoriae are borne along on thick masses of ice, but they likewise exercise a
constant action, while the volcano is in a state of perfect repose, by
infiltration into the fissures of the trachytic rock. Cavities which are
either on the declivity or at the foot of the mountain are gradually
converted into subterranean resevoirs of water, which communicate by
numerous narrow openings with mountain streams, as we see exemplified in the
highlands of Quito. the fishes of these rivulets multiply, especially in
the obscurity of the hollows; and when the shocks of earthquakes, which
precede all eruptions in the andes, have violently shaken the whole mass of
the volcano, these subterranean caverns are suddenly opened, and water,
fishes, and tufaceous mud are all ejected together. It is through this
singular phenomenon* that the inhabitants of the highlands of Quito became
acquainted with the existence of the little cyclopic fishes, termed by them
the prenadilla.
[footnote] *Pimelodes cyclopum. See Humboldt, 'Recueil d'Observations de
Zoologie et d'Anatomie Comparee', t. i., p. 21-25.
On the night between the 19th and 20th of June, 1698, when the summit of
Carguairazo, a mountain 19,720 feet in height, fell in, leaving only two
huge masses of rock remaining of the ledge of the crater, a space of nearly
thirty-two square miles was overflowed and devastated by streams of liquid
tufa and argillaceous mud ('lodazales'), containing large quantities of dead
fish.
p 233
In like manner, the putrid fever, which raged seven years previously in the
mountain town of Ibarra, north of Quito, was ascribed to the ejection of
fish from the volcano of Imbaburu.*
[footnote] *[It would appear, as there is no doubt that these fishes
proceed from the mountain itself, that there must be large lakes in the
interior, which in ordinary season are out of the immediate influence of the
volcanic action. See Daubeney, op. cit., p. 488, 497.] -- Tr.
Water and mud, which flow not from the crater itself, but from the hollows
in the trachytic mass of the mountain, can not, strictly speaking, be
classed among volcanic phenomena. They are only indirectly connected with
the volcanic activity of the mountain, resembling, in that respect, the
singular meteorological process which I have designated in my earlier
writings by the term of 'volcanic storm'. The hot stream which rises from
the crater during the eruption and spreads itself in the atmosphere,
condenses into a cloud, and surrounds the column of fire and cinders which
rises to an altitude of many thousand feet. The sudden condensation of the
vapors, and, as Gay-Lussac has shown, the formation of a cloud of enormous
extent, increase the electric tension. Forked lightning flashes from the
column of cinders, and it is then easy to distinguish (as at the close of
the eruption of Mount Vesuvius, in the latter end of October, 1822) the
rolling thunder of the volcanic storm from the detonations in the interior
of the mountain. the flashes of lightning that darted from the volcanic
cloud of steam, as we learn from Olafsen's report, killed eleven horses and
two men, on the eruption of the volcano of Katlagia, in Iceland, on the 17th
of October, 1755.
Having thus delineated the structure and dynamic activity of volcanoes, it
now remains for us to throw a glance at the differences existing in their
material products. The subterranean forces sever old combinations of matter
in order to produce new ones, and they also continue to act upon matter as
long as it is in a state of liquefaction from heat, and capable of being
displaced. The greater or less pressure under which merely softened or
wholly liquid fluids are solidified, appears to constitute the main
difference in the formation of Plutonic and volcanic rocks. The mineral
mass which flows in narrow, elongated streams from a volcanic opening (an
earth-spring), is called lava. where many such currents meet and are
arrested in their course, they expand in width, filling large basins, in
which they become solidified in superimposed strata. These few sentences
describe the general character of the products of volcanic activity.
p 234
Rocks which are merely broken through by the volcanic action are often
inclosed in the igneous products. Thus i have found angular fragments of
feldspathic syenite imbedded in the black augitic lava of the volcano of
Jorullo, in Mexico; but the masses of dolomite and granular limestone, which
contain magnificent clusters of crystalling fossils (vesuvian and garnets,
covered with mejonite, nepheline, and sodalite), are not the ejected
products of Vesuvius, these belonging rather to very generally distributed
formations, viz., strata of tufa, which are more ancient than the elevation
of the Somma and of Vesuvius, and are probably the products of a deep-seated
and concealed submarine volcanic action.*
[footnote] *Leop. von Buch, in Poggend., 'Annalen', bd. xxxvii., s. 179.
We find five metals among the products of existing volcanoes, iron, copper,
lead, arsenic, and selenium, discovered by Stromeyer in the crater of
Volcano.*
[footnote] *[The little island of Volcano is separated from Lipari by a
narrow channel. It appears to have exhibited strong signs of volcanic
activity long before the Christian era, and still emits gaseous exhalations.
Stromeyer detected the presence of selenium in a mixture of sal ammoniac
and sulphur. Another product, supposed to be peculiar to this volcano, is
boracic acid, which lines the sides of the cavities in beautiful white silky
crystals. Daubeney, op. cit., p. 257.] -- Tr.
The vapors that rise from the 'fumarolles' cause the sublimation of the
chlorids of iron, copper, lead, and ammonium; iron glanceI and chlorid of
sodium (the latter often in large quantities) fill the cavities of recent
lava streams and the fissures of the margin of the crater.
[footnote] *Regarding the chemical origin of iron glance in volcanic
masses, see Mitscherlich, in Poggend., 'Annalen', bd. xv., s. 630; and on
the liberation of hydrochloric acid in the crater, see Gay-Lussac, in the
'Annals de Chimique et de Physique', t. xxii., p. 423.
The mineral composition of lava differs according to the nature of the
crystalline rock of which the volcano is formed, the height of the point
where the eruption occurs, whether at the foot of the mountain or in the
neighborhood of the crater, and the condition of temperature of the
interior. Vitreous volcanic formations, obsidian, pearl-stone, and pumice,
are entirely wanting in some volcanoes, while in the case of others they
only proceed from the crater, or, at any rate, from very considerable
heights. These important and involved relations can only be explained by
very accurate crystallographic and chemical investigations. My
fellow-traveler in Siberia, Gustav Rose, and subsequently Hermann Abich,
have already been able, by their fortunate and ingenious researches, to
throw much light on the structural relations of the various kinds of
volcanic rocks.
p 235
The greater part of the ascending vapor is mere steam. When condensed, this
forms springs, as in Pantellaria,Iwhere they are used by the goatherds of
the island.
[footnote] *[Steam issues from many parts of this insular mountain, and
several hot springs gush forth from it, which form together a lake 6000 feet
in circumference. Daubeney, op. cit.] -- Tr.
On the morning of the 26th of October, 1822, a current was seen to flow from
a lateral fissure of the crater of Vesuvius, and was loong supposed to have
been boiling water; it was, however, shown, by Monticelli's accurate
investigations, to consist of dry ashes, which fell like sand, and of lava
pulverized by friction. The ashes, which sometimes darken the air for hours
and days together, and produce great injury to the vineyards and olive
groves by adhering to the leaves, indicate by their columnar ascent,
impelled by vapors, the termination of every great eqrthquake. This is the
magnificent phenomenon which Pliny the younger, in his celebrated letter to
Cornelius Tacitus, compares, in the case of Vesuvius, to the form of a lofty
and thickly-branched and foliaceous pine. That which is described as flames
in the eruption of scoriae, and the radiance of the glowing red clouds that
hover over the crater, can not be ascribed to the effect of hydrogen gas in
a state of combustion. They are rather reflections of light which issue
from molten masses, projected high in the air, and also reflections from the
burning depths, whence the glowing vapors ascend. We will not, however,
attempt to decide the nature of the flames, which are occasionally seen now,
as in the time of Strabo, to rise from the deep sea during the activity of
littoral volcanoes, or shortly before the elevation of a volcanic island.
When the questions are asked, what is it that burns in the volcano? what
excites the heat, fuses together earths and metals, and imparts to lava
currents of thick layers a degree of heat that lasts for many years? it is
necessarily implied that volcanoes must be connected with the existence of
substances capable of maintaining combustion, like the beds of coal in
subterranean fires.
[footnote] *See the beautiful experiments on the cooling of masses of rock,
in Bischof's 'Warmelehre', s. 384, 443, 500-512.
According to the different phases of chemical science, bitumen, pyrites, the
moist admixture of finely-pulverized sulphur and iron, pyrophoric
substances, and the metals of the alkalies and earths, have in turn been
designated as the cause of intensely active volcanic phenomena. The great
chemist, Sir Humphrey Davy, to whom we are indebted for the knowledge of the
most combustible metallic
p 236
substances, has himself renounced his bold chemical hypothesis in his last
work ('Consolation in Travel, and last Days of a Philosopher') -- a work
which can not fail to excite in the reader a feeling of the deepest
melancholy. the great mean density of the earth (5.44), when compared with
the specific weight of potassium (0.865), of sodium (-.972), or of the
metals of the earths (1.2), and the absence of hydrogen gas in the gaseous
emanations from the fissures of craters, and from still warm streams of
lava, besides many chemical considerations, stand in opposition with the
earlier conjectures of Davy and Ampere.*
[footnote] *See Berzelius and Wohler, in Poggend., 'Annalen', bd. i., s.
221, and bd. xi., s. 146; Gay-Lussac, in the 'Annals de Chimie', t. x.,
xii., p. 422; and Bischof's 'Reasons against the Chemical Theory of
Volcanoes', in the English edition of his 'Warmelehre', p. 297-309.
If hydrogen were evolved from erupted lava, how great must be the quantity
of the gas disengaged, when, the seat of the volcanic activity being very
low, as in the case of the remarkable eruption at the foot of the Skaptar
Jokul in Iceland (from the 11th of June to the 3d of August, 1783, described
by Mackenzie and Soemund Magnussen), a space of many square miles was
covered by streams of lava, accumulated to the thickness of several hundred
feet! Similar difficulties are opposed to the assumption of the penetration
of the atmospheric air into the crater, or, as it is figuratively expressed,
the 'inhalation of the earth', when we have regard to the small quantity of
nitrogen emitted. So general, deep-seated, and far-propagated an activity
as that of volcanoes, can not assuredly have its source in chemical
affinity, or in the mere contact of individual or merely locally distributed
substances. Modern geognosy* rather seeks the cause of this activity in the
increased temperature with the increase of depth at all degrees of latitude,
in that powerful internal heat which our planet owes to its first
solidification, its formation in the regions of space, and to the spherical
contraction of
p 237
matter revolving elliptically in a gaseous condition.
[footnote] *[On the various theories that have been advanced in explanation
of volcanic action, see Daubeney 'On Volcanoes', a work to which we have
made continual reference during the preceding pages, as it constitutes the
most recent and perfect compendium of all the important facts relating to
this subject, and is peculiarly adapted to serve as a source of reference to
the 'Cosmos', since the learned author in many instances enters into a full
exposition of the views advanced by Baron Humboldt. The appendix contains
several valuable notes with reference to the most recent works that have
appeared on the Continent, on subjects relating to volcanoes; among others,
an interesting notice of Professor Bischof's views "on the origin of the
carbonic acid discharged from volcanoes," as enounced in his recently
published work, 'Lehrbuch der Chemischen und Physikalischen Geologie'.] --
Tr.
We have thus mere conjecture and supposition side by side with certain
knowledge. A philosophical study of nature strives ever to elevate itself
above the narrow requirements of mere natural description, and does not
consist, as we have already remarked, in the mere accumulation of isolated
facts. The inquiring and active spirit of man must be suffered to pass from
the present to the past, to conjecture all that can not yet be known with
certainty, and still to dwell with pleasure on the ancient myths of geognosy
which are presented to us under so many various forms. If we consider
volcanoes as irregular intermittent springs, emitting a fluid mixture of
oxydized metals, alkalies, and earths, flowing gently and calmy wherever
then find a passage, or being upheaved by the powerful expansive force of
vapors, we are involuntarily led to remember the geognostic visions of
Plato, according to which hot springs, as well as all volcanic igneous
streams, were eruptions that might be traced back to one generally
distributed subterranean cause, 'Pyriphlegethon'.*